Television picture tube inner shielding material having a blackened layer of superior adhesion and method of manufacturing the same

Abstract

An inner shielding material and a method of manufacturing the same, wherein the material comprises a steel sheet 0.10 to 0.25 mm thick of a composition of ≦0.005% C, ≦2.0% Si, ≦0.4% P, 0.1 to 1.0% Mn, 0.01% S, ≦0.01% sol.Al, ≦0.01% N and the balance Fe and residual impurities, having a hardness H v (500 g) of 90 or greater and a grain size of 7 or less when measured by ferrite grain size; and a blackened layer on the surface of the steel sheet comprising primarily FeO formed by transformation of Fe 3 O 4 and having superior adhesion.

We claim: 
     
       1. An inner shielding material comprising: a steel sheet 0.10 to 0.25 mm thick of a composition in weight percent of ≦0.005% C, ≦2.0% Si, ≦0.4% P, 0.1 to 1.0% Mn, ≦0.01% S, ≦0.01% sol.Al, ≦0.01% N and the balance Fe and residual impurities, having a hardness H V  (500 g) of 90 or greater and a grain size of 7 or less when measured by ferrite grain size; and   a blackened layer on the surface of the steel sheet comprising FeO formed by transformation of Fe 3  O 4  and having superior adhesion.   
     
     
       2. The inner shielding material of claim 1 which has a magnetic permeability of 750 emu or greater in a direct current magnetic field of 0.3 Oe and a coercive force of 1.2 Oe or less at a maximum magnetization force of 10 Oe. 
     
     
       3. A method of fabricating inner shielding material comprising:  preparing a slab of a composition of ≦0.005% C, ≦2.0% Si, ≦0.4% P, 0.1 to ≦1.0% Mn, 0.01% S, ≦0.1% sol.Al, ≦0.01% N and the balance Fe and residual impurities;   fabricating a hot-rolled sheet from the slab;   cold rolling the hot-rolled sheet to a thickness of 0.10 to 0.25 mm;   continuously annealing the cold-rolled sheet; and   first forming on the surface of the cold-rolled sheet an oxide film comprised of Fe 3  O 4  by employing an oxidizing gas atmosphere over part or all of the course of the continuous annealing in which the temperature rises from 300° C. to 750° C., and then switching to a non-oxidizing gas atmosphere to carry out soaking treatment, after which cooling is effected in a non-oxidizing atmosphere;   whereby a blackened layer comprising FeO is formed.   
     
     
       4. The inner shielding material of claim 1 in which the blackened layer is FeO formed by transformation of 80% or more of the Fe 3  O 4 .